This project was initiated to identify those polypeptides that specifically relate to the metastatic process as the first step toward their purification and identification. Utilization of metastasizing and non-metastasizing cells derived from the same parent population of tumor cells is fundamental to this project. We have confirmed that the TMT-081-MS cells do metastasize in syngeneic rats and that the TMT-081-NM cells do not metastasize in syngeneic rats. Radiolabelling of these cells with 14-C amino acids has revealed several qualitative and quantitative differences in their polypeptide patterns. The most intensely labelled spots that occurred in the TMT-081-MS cells were (MW/pI) 67/5.5 and 50/4.5 and the most intense spots that occurred only in the TMT- 081-NM cells were 46/6.7 and 38/6.1. When a 32-P-radiolabel was used with these cells, a number of polypeptides could be observed that were not located from the 14-C labelling. The most intensely 32-P labelled spots occurring only in the metastatic cells were 98/4.7 and 24/4.5. Those polypeptides that were approximately threefold greater in intensity in the metastatic cells compared to the non-metastatic cell: were 14/5.2, 15/5.4 and 12/6.3. The polypeptides of 40/5.9 and 40/5.8 were at least threefold greater in the intensity of 32-P label compared to the corresponding polypeptides in the metastatic cells. A number of subclones of the metastasizing TMT-081-MS cells have been derived from metastasis in Wistar/Furth rats. These subclones possess metastatic capacity and will be used in further experiments.